Generally, a helical antenna includes a ground plane, a radiator structure with a helically shaped conductor, and a mounting structure that establishes and maintains a desired orientation between the radiator structure and the ground plane. There are two types of radiator structures prevalent in helical antennas. The first type of radiator structure comprises a self-supporting helically-shaped conductor that is made of a relatively stiff metal and, as such, is capable of holding its helical shape when subjected to no more than a predetermined force (e.g., gravity). The second type of radiator structure comprises a helical shaped conductor and a dielectric structure that supports the conductor in the helical shape when subjected to no more than a predetermined force.
The method of manufacturing the first type of radiator structure typically involves providing a form with an exterior surface that defines the general shape (e.g., conical or cylindrical) of the helix conductor and a path marked on or associated with the exterior surface that defines the helical path of the conductor on the exterior of the form. For example, the form may have a cylindrical exterior surface with a helical groove established in the cylindrical exterior surface. A relatively stiff wire is wound around the form in accordance with the defined helical path associated with the form. For instance, if the form bears a helical groove, the wire is wound around the form such that the wire is established in the helical groove. After the wire has been wound around the form, the wire and the form are separated from one another. In the case of a cylinder with a helical groove, the cylinder and the helically shaped wire may be “unscrewed” from one another. In any event, the helically shaped wire is a radiator structure suitable for integration into a helical antenna. This approach to manufacturing the first type of radiator structure commonly requires significant effort in designing the form and the process for separating the form from the helically shaped wire to address, for example, issues related to elastic recovery or springback, i.e., the tendency of the wire to want to deform to some extent towards its original shape.
Several methods have been devised for manufacturing the second type of radiator structure. One method for manufacturing this type of radiator structure involves the creation of a dielectric frame that defines the overall shape of radiator structure (e.g., cylindrical or conical). Such a dielectric frame can take many forms. Among the various types of dielectric frames are: (a) mast and spar frames that include a main mast from which spars extend that engage the conductor at discrete locations and support the wire in the desired helical shape, (b) crossed and notched templates with the notches situated to engage the wire and support the wire in the desired helical shape, and (c) forms with exterior surfaces that have the desired overall shape for the conductor and, typically, a structure that defines the helical path of the conductor about the exterior surface (e.g., a cylinder with helical groove established in the exterior surface). A conductor is engaged to the frame so as to have the desired helical shape. The dielectric frame and the helically shape conductor constitute a radiator structure.
A second approach for manufacturing the second type of helical antenna element is to establish one or more conductive strips on a flexible and planar dielectric substrate. Typically, the conductive strips are established on the substrate by a photolithographic process. Subsequently, separate portions of the edge of the substrate are brought together so as to place the substrate into the desired shape (e.g., a cylinder or right circular cone). The separate portions of the edge of the substrate typically butt up against one another or overlap with one another to form a seam and are fixed in place. In many cases, the conductive strips are used to form one or more helices that are each comprised of multiple turns. For such helical antenna elements, the ends of each of the strips that are intermediate to the terminal ends of a helix must be electrically connected to one another at a point adjacent to the seam.
A third approach for manufacturing the second type of radiator structure involves providing a dielectric frame with an exterior surface. A portion of the exterior surface defines the desired helical shape of one or more electrical conductors. For example, a portion of the exterior surface may define a groove with the desired helical shape. The exterior surface of the dielectric frame is plated with an electrically conductive material and then processed so as to remove the plating that is not associated with the desired helical shape.
Yet another approach to manufacturing the second type of radiator structure includes providing a form with an exterior surface that has the overall desired shape for the helical antenna element (e.g., a cylinder), winding a polystyrene sheathed wire around the form so that the wire follows the desired helical path, applying heat to the polystyrene sheathed wire to thermo-fix the polystyrene sheathed wire in the desired helical shape, and then separating the form and the thermo-fixed polystyrene wire from one another.